Early and late histologic changes in saphenous vein coronary artery bypass grafts have been reported by numerous authors. Subendothelial cellular proliferation has led to graft failure in some cases. A study was undertaken to determine whether the angle of the aortosaphenous vein anastomosis influences the degree of subendothelial proliferation. Thirteen dogs survived aortocoronary bypass to the left circumflex coronary artery. The angle of aortic anastomosis was acute in 5 dogs, perpendicular in 2 dogs, and obtuse in 6 dogs. Angiograms demonstrated open grafts at least six months following operation in 12 of the 13 dogs. All the dogs have been killed, and the hearts perfusion-fixed. Histologic examination of the vein grafts is pending.